1. Field of the Invention
The present invention relates to a device which indicates the safety limits of the air pressure in the pneumatic tires of a vehicle by transmitting information from the rotating wheel to the driving control board.
The operation of the device is based on a capacitive coupling between rotating and nonrotating conductive (metallic, carbon, etc.) coaxial cylindrical, coaxial annular and concentric annular surfaces mounted onto insulated bases. They are fixed into any available and suitable space between the rotating and the nonrotating part of the wheel assembly, which can be the space between the rotating bearing flange and nonrotating braking system or the space between the bearings of the wheel.
For each one of the wheels of the vehicle the system includes a tire pressure sensor mounted on the wheel which operates as an ON-OFF mechanical switch, according to the variations of the air pressure in the pneumatic tires. When the air pressure, in any one of the pneumatic tires of the vehicle, deviates from a normal predetermined value, the tire pressure sensor electrically connects the rotating conductive surfaces, thereby effecting an enhanced capacitive coupling between the above mentioned conductive surfaces which can be detected by an electronic circuit, by means of a visual or audio indication.
Over-or under-inflated tires are dangerous and could be avoided by the device of the present invention, which can operate as a road safety device.
The present invention eliminates all the disadvantages of the various patents which have been awarded in the past to the same inventor N. F. Tsagas from U.S. Pat. No. 5,531,109/Jul. 2, 1996, EPO 550701 B1/Oct. 16, 1995 and Australia 671583/May 3, 1997.
2. Description of the Prior Art
Various devices have been developed in the prior art to control the faulty air pressure in anyone of the tires of a vehicle. Basically the following principles of operation are used in those prior art devices.
a) The current collector system, wherein a current collector ring is used on the rotating part of the wheel and a collector brush is fixed at the nonrotating part of the wheel assembly to connect the tire pressure sensor and indicator of the device.
b) The wireless system, wherein a wireless frequency transmitter is mounted on the rotating part of the wheel, and a receiver is placed at the driving control board.
c) Resonance circuit system, wherein a detecting switch, an antenna and a circuit with inductance and capacitance are mounted onto the rotating tire and a transmitter and receiver at the nonrotating part of the vehicle, wherein an intermittent retransmission of the abovementioned circuit occurs in response to the variations in tire air pressure, this retransmission being of the same frequency as the resonance frequency of the circuit
Various disadvantages are associated with the aforementioned systems of the prior art, wherein degradation of performance tends to occur, sooner or later, due to a) wear of the parts, b) batteries mounted onto the rotating wheels, c) integrated electronic circuits for the transmitter which are sensitive to the strains mounted onto the rotating wheels, d) complicate mechanism which tends to exhibit deviations in resonance and in general e) the installation of systems which make the device unreliable, under worsh conditions and needs employment of severe maintenance standards.
In the previous Tsagas""s systems described in the aforementioned patents, various disadvantages being due to improper shape and locality of metallic strips, the electronic circuit and the pressure gauge made the device unreliable and caused installation difficulties.
The first object of the present invention is to provide an air pressure monitoring device in the pneumatic tires of a vehicle, which eliminates all the abovementioned disadvantages in order to achieve a) an accurate and reliable operation, b) a convenient and easy installation, c) a low cost with maintenance requirements close to zero and d) an additional safety capability to the driver.
A second object of the present invention is to provide an air pressure monitoring device in the pneumatic tires of a vehicle, with a special configuration and dimensions of rotating and nonrotating conductive coaxial cylindrical and annular surfaces within the wheel assembly, in order to achieve the highest possible capacity of the nonrotating conductive surfaces by shorting out the rotating conductive, metallic or carbon, surfaces and to eliminate parasitic capacitances.
A third object of the present invention is to provide a proper positioning for the conductive surfaces within the wheel assembly, so as to offer protection from temperature, humidity, water, dust, etc.
The fourth object of the present invention is to provide a proper electronic circuit so as to obtain optimum efficiency in the operation of the device in the desired limits of capacity changes.
Finally, a fifth object of the present invention is to provide a reliable tire pressure sensor of very small dimensions to operate as a mechanical switch of shorting out the rotating conductive surfaces after exceeding the safety limits of air pressure in the pneumatic tires of a vehicle.
The abovementioned objects of the present invention are implemented with the use of rotating conductive coaxial and concentric cylindrical and annular surfaces surrounding the nonrotating conductive cylindrical and annular surfaces mounted, rotating and nonrotating surfaces, onto insulated bases or metallic bases insulated by ceramic. They are fixed onto the rotating and nonrotating parts of the wheel assembly, in the location between the bearing flange and braking system and between the bearings of the wheel form cylindrical and plane air capacitors. An air pressure sensor, as a tire pressure sensor, of a vehicle operating as an ON-OFF mechanical switch can electrically short out the rotating conductive cylindrical and annular surfaces by means of a silicon membrane being curved accordingly to the air pressure changes. This tire pressure sensor can be positioned either on the existing valves or on a hiding place of the rim. The capacitance increase of nonrotating conductive surfaces, by shorting out the rotating conductive surfaces, can change the operating frequency of the electronic circuit. This can activate visual and audio indications corresponding to the tire with the faulty pressure.
One of the main advantages of the present invention is the coaxial and concentric cylindrical and annular configuration of the rotating conductive surfaces mounted onto insulated bases and surrounding the cylindrical and annular nonrotating conductive surfaces being mounted, by metal or carbon-plated, into shallow circular channels, which are opened onto the periphery of insulated bases. Some nonconductive concentric rings with negligible friction coefficient like ceramic and with small thickness surround and cover the conductive concentric annular surfaces and a spring is pressing the insulated base from back side. By this configuration the rotating and nonrotating conductive surfaces can be very close, in a constant distance, without touching each other. This coaxial cylindrical and annular configuration of conductive surfaces together with their proper positioning onto the insulated bases results to a maximum enhanced capacitive coupling between the abovementioned conductive surfaces, which thereby increases very much the operational efficiency of the device. Also the parasitic capacitances, due to mechanical defaults and vibrations of the rotating wheels, dust, water, humidity, temperature, surrounding metallic surfaces etc, are negligible.